Problem: Nadia ate 2 slices of pizza. Luis ate 4 slices. If Nadia ate $\dfrac{2}{9}$ of the pizza, what fraction of the pizza was eaten?
Explanation: If 2 slices represent $\dfrac{2}{9}$ of the pizza, there must have been a total of 9 slices. $\text{fraction of pizza eaten} = \dfrac{\text{number of slices eaten}}{\text{number of slices total}}$ They ate ${6}$ out of $9$ slices. They ate $\dfrac{6}{9}$ of the pizza.